Rappers are electromechanical devices which are used for mechanically and periodically cleaning dust from surfaces. During the operation of electrostatic precipitators, electronic filters or dust collectors, the collector plates, electrodes or other components must be cleaned by electromechanical rappers to remove the dust which has accumulated on these surfaces. In general, a rapper consists of a hammer that mechanically hits a surface to be cleaned or an anvil which is connected to the surface to be cleaned. The shock caused by the hitting hammer causes the dislodging of the dust.
U.S. Pat. No. 4,767,423 discloses a rapping mechanism which is used in electrostatic precipitators. In the disclosed mechanism, a spring or a drop hammer is provided behind a cylindrical hammer in order to increase the impact force of the hammer. The spring or the drop hammer may be mounted so that it can be swung from an inoperative position to an operative position in case an additional impact force is needed. In an operative position, the impact force is increased due to the added mass of the drop hammer or due to the elastic force of the spring.
Canadian patent No. 1129788 describes a rapping apparatus for an electrostatic precipitator. A free-fall hammer is attached to a rotating shaft so that it falls against an anvil from a top dead centre position. The size and the weight of this tumbling hammer is selected to obtain the desired maximum rapping intensity with a free fall. In order to vary or decrease the rapping intensity, an attenuator plate is located within the free-fall area of the hammer. By intercepting the hammer during its downfall and subsequently releasing it, the impact force is reduced to its desired amount. The attenuator plate is adjustable to modify the rapping intensity.
The correct balance of rapping intensity, duration and frequency is essential to an optimum precipitator performance. Inadequate cleaning of discharge electrodes and collecting plates is a dominating cause of poor precipitator performance, resulting in increased sparking, reduced power to the precipitator and higher emissions. The increasingly stringent controls on industrial emission lead to strengthened efforts to develop highly effective precipitators.
In both the U.S. Pat. No. 4,767,423 describing an electromagnetic rapper and the Canadian patent No. 1129788 describing a tumbling hammer the intensity of the impact force of the hammer can be varied by mechanical devices like a drop hammer or a spring to increase the impact force or an attenuator plate to decrease the impact force. However, the implementation of these mechanical devices can prove to be complex and expensive with regard to installation and maintenance.